1. Field of the Invention
The present invention relates to filter elements and to the machines and methods used in their manufacture.
2. Background Information
There are machines used to manufacture tubular filter elements in a continuous process. U.S. Pat. No. 4,101,423 discloses a tubular filter element made on a single-stage multiple winding machine of helically wound and overlapping layers such as an inner layer of high wet strength, highly porous paper, a second layer of thin microporous filtration material of a sterilizing grade and an outer layer of a porous sheet of expanded polyethylene and an outer porous layer to support the filtration material. The layers are wrapped on a fixed mandrel to be self-overlapping in a single layer overlap and advance in unison along the mandrel as they are wrapped so that there is no relative motion between the adjacent layers of the laminate. An adhesive material that blocks the passage of the particulate matter and bacteria being filtered seals the second filtration layer in the region of overlap. The ends of the tubular laminate construction are impregnated over a predetermined length adjacent to each edge of the construction with a suitable sealing adhesive material such as a polyurethane potting compound. When the adhesive material cures, the end portions provide mechanical support for the tube while blocking the passage of the fluid or the particulate and bacterial contaminants. (See Col. 5, Ins. 4-26.)
A circularly wound spiralled chromatographic column is shown in U.S. Pat. No. 4,986,909. Here, a sandwich or laminate of alternating layers of swellable fibrous matrix in sheet form and layers of spacer means, with the periphery of the sandwich is compressed into a fluid-tight configuration. Typically, the peripheral edges of alternating discs of swellable fibrous matrix and spacer means are joined. Preferably, the fibrous matrix contains or has bonded therein a thermoplastic polymeric material, as does the spacer means. The edges may be joined by appropriate heating, e.g. sonic welding. (See Col. 10, Ins. 40-61.)
Another spirally, circularly wound filter element is disclosed in U.S. Pat. No. 5,114,582 and comprises one or more filter elements spirally wound on a cylindrical permeate transport tube. Each filter element comprises a heat-sealed membrane element and a feed spacer. (See Abstract.)
A process for the manufacture of porous tubes of high permeability made from a carbon-carbon composite material in a strip of mat spirally wound on a mandrel is disclosed in U.S. Pat. No. 5,264,162. Porous tubes are made from said material by winding over a mandrel a nonwoven sheet, made from a carbon fiber precursor, followed by compression and hot stabilization of the assembly. The sheet is impregnated by a resin, followed by a thermal carbonization treatment of the resin. Tubes are obtained having a high permeability, small pore diameter and an inner surface of low rugosity. (See Abstract.) Also disclosed is the use of successive mat layers, making it possible to obtain, in the final tube, pore diameters which increase in the direction of the flux to be filtered, generally from the inside towards the outside of the tube. It is advantageous that these pore diameters are substantially in a ratio of 10 between one layer and the next, which may be obtained by adjusting the density of the mat and/or the diameter of the fibers. (See Col. 4, Ins. 10-20.)
A helically wound, single wrap filter element is disclosed in U.S. Pat. No. 5,409,515, including a porous membrane of a polytetrafluoroethylene and one or more sheets composed of fibers made of a thermally melting synthetic resin. (See Abstract.) The sheets are thermally fused over a selected length. (See Col. Ins. 40-46.)